REVIEWS 459 



He cites at the outset a difficulty, "perhaps more apparent than 

 real," encountered by the newer hypothesis in the sporadic arrange- 

 ment of the meteoric material which, if like known meteorites, would 

 differ from the existing surface rocks. This difficulty, however, loses 

 much, if not all, of its force when the effects of volcanic action are 

 considered. The hypothesis assumes that the interior heat which 

 arises from compression gives rise to the melting of certain constitu- 

 ents of the rock mass, and that these, previous to eruption, undergo 

 magmatic differentiation into the well-known igneous rocks and prob- 

 ably into others which are but rarely ejected because of their high 

 specific gravity, as the iron-bearing basalt of Disco Island, Greenland, 

 and other extremely basic rocks of the ferro-magnesian type. Volcanic 

 action is assumed to have begun effectively before the growing earth 

 reached the size of the moon and all accretions subsequently made 

 would be more or less invaded and overflown by igneous intrusions 

 and extrusions of differentiated lava. In the closing stages of the 

 earth's growth, the infall of meteoric matter declined gradually to an 

 inappreciable amount, while the volcanic action is thought to have 

 continued with relative vigor for a notable period after the essential 

 cessation of growth, and to have perpetuated itself in less activity 

 down to the present time. If the moon may be taken as an illustra- 

 tion of the prevalence and effectiveness of surface vulcanism in a body 

 one eightieth of the earth's mass, it does not seem violent to suppose 

 that the original meteoric matter of the earth would be deeply buried 

 under surface lava flows and tuffs in the closing stages of its growth. 

 Recent studies in the Lake Superior region, in Scandinavia, and in 

 Lapland seem to concur in showing that the oldest known rocks con- 

 sist of such lava flows and pyroclastic layers associated with some 

 small amounts of ordinary clastic material, all mashed into schistos- 

 ity. Into these schists, the great granitic series were intruded. Under 

 the newer hypothesis these intrusions are to be regarded as merely 

 a continuation of the earlier active vulcanism which was then more 

 largely basic, but which had now, in the progress of magmatic differ- 

 entiation, attained a dominant acidic character, perhaps as the partial 

 complement of the earlier basic flows of the schist series or of the later 

 basic flows of the Algonkian. The " fundamental gneiss " does not, 

 therefore, appear, in the light of these recent studies, to be funda- 

 mental, nor does the "basement complex" appear to be basal. These 

 recent investigations seem to bring the Archean series into almost 



